Collocations for gentle - adj.

appear, be, look, seem
become

extremely, fairly, very, etc.
almost
surprisingly
deceptively
His mouth looked deceptively gentle.

on
The new treatments are gentle on your hair.

with
She was very gentle with the children.

Gentle is used with these nouns:
bend, breeze, caress, character, curve, decline, descent, disposition, dive, embrace, encouragement, exercise, finger, gradient, grip, guidance, hand, handling, heat, hill, hint, hum, humour, irony, kiss, knock, light, massage, melody, motion, movement, nudge, pace, person, persuasion, pressure, pull, push, rain, rebuke, reminder, reprimand, rustle, sex, shake, shampoo, shove, slap, slope, smile, soap, soul, squeeze, stretch, stroll, swell, tap, tinkle, tone, touch, trot, tug, voice, walk, warmth, wave, whisper, wit